Biology subjects

Herath, J.

Publications and source records attributed to Herath, J..

5 recordsLinked to original sources

bioRxiv2023

Emerging Threat of Ranavirus: Prevalence, Genetic Diversity, and Climatic Drivers of Ranavirus (Family Iridoviridae) in ectothermic vertebrates of Asia

Ranavirus disease, caused by viruses within the genus Ranavirus (family Iridoviridae), is considered a globally emerging infectious disease linked to mass mortality events in both wild and cultured ectothermic vertebrates. Surveillance work is however limited in Asia hence prevalence and the dynamics of the disease remains poorly understood. To understand disease burden and the potential biotic and abiotic drivers in southern China region, we conducted a systematic surveillance of the ranavirus across Guangxi Zhuang Autonomous region (GAR). For this, we used a multifaceted approach involving screening of amphibians and other potential reservoirs, diagnostic tests, phylogenetic analyses, prevalence estimation, co-infection assessments, and climatic niche analyses. Over one thousand individuals were sampled across 25 sampling sites. We found ninety-two individuals from 18 species of ectothermic vertebrates to be infected with ranavirus. Two lineages were responsible - Rana nigromaculata ranavirus and Tiger frog virus were identified using phylogenetic analysis based on the major capsid protein (MCP) gene fragment. We also found evidence of a co-infection with ranavirus and Bd that can be highly detrimental to host populations; possibly the first such documentation in Asia. Our niche modelling analysis suggests that precipitation and seasonality play an important role in ranavirus prevalence in Guangxi region - southwestern, southeastern, central and northeastern regions of GAR can be considered to be optimum habitats for ranaviruses. Infection rates in wild frog species have reached 100% in some areas, even in nature reserves. Our research also indicates that culture facilities and pet farms are frequently infected, serving as likely vectors for the regional and global spread of ranaviruses. The knowledge generated suggests the need for systematic surveillance, stringent biosecurity measures, and control of international animal trade to prevent further transmission and protection of biodiversity and aquaculture industries across Asia.

ecology↗

bioRxiv2023

New climatically specialized lineages of Batrachochytrium dendrobatidis and their sub-lethal effects on amphibians establish the Asiatic origins of the pathogen

Chytridiomycosis, a highly significant global wildlife disease, has caused unprecedented amphibian population declines and species extinctions worldwide. In contrast, mass die-offs due to chytridiomycosis have not been observed in Asia, which is thought to be the ancestral region of origin and a hyper-diversity hotspot of the known causal pathogens, Batrachochytrium dendrobtidis (Bd) and B. salamndrivorans (Bsal). It has been hypothesized that Asian amphibians may have evolved immunity to clinical Batrachochytrium infection. However, limited knowledge of endemic lineages, evolutionary history, and climate-related infection patterns limits our ability to explore this hypothesis. Here, we investigated the genetic diversity and infection patterns of the frog-infecting species, Bd, in Chinas poorly-explored Guangxi region. We used the internal transcribed spacer (ITS) marker and the nested PCR method to survey prevalence and haplotype diversity of Bd across 17 forest sites. A generalized linear model was used to evaluate associations between numerous variables and Bd prevalence within native amphibians. Our results identified seven new haplotypes, four of which are closely related to the early-emerging BdASIA-1 lineage recovered from South Korea. We also identified a unique Asian haplotype, close to the BdASIA-3 lineage, as the most prevalent (64.6% of Bd-infected adult individuals) in 11 out of 15 infected species. This haplotype was also detected in a salamander individual, which exhibited non-lethal skin lesions on the abdomen. The infection of Bd within amphibians was found to be positively associated with temperature and elevation. Our findings suggest that there is significant undiscovered genetic diversity of Asian Bd lineages in this region. Longer-term studies are required to further investigate Bd diversity, prevalence, seasonality and impact on native species and populations in Southern China and across the region of origin in Asia. Author SummaryChytridiomycosis is a disease which is responsible for the sharp decline of amphibian populations and species extinctions around the world. Surprisingly, it has not yet been well-studied in Asia, the region where the two causal pathogens of the disease, Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal) originated. In order to better understand the lack of mass die-offs in Asia, we recently conducted a study in south Chinas Guangxi region to investigate the genetic diversity and infection patterns of Bd. Through the use of internal transcribed spacer (ITS) markers and nested PCR, we discovered seven new types of Bd, four of which were closely related to the early-emerging BdASIA-1 lineage from South Korea. The highest prevalence of Bd infection was observed in 11 species of amphibians, including a salamander which had non-lethal skin lesions. It was also noted that infection of Bd in amphibians was associated with temperature and elevation. This study has provided important information on Bd diversity and prevalence in the region, and further research is needed to explore Asia as the putative region of origin for this disease.

evolutionary biology↗

bioRxiv2022

Climatic niche evolution of infectious diseases driving amphibian declines

Climate change and infectious diseases continue to drive global amphibian population declines, contributing to one of the greatest vertebrate extinctions of the Anthropocene. Currently around 16% amphibian species across the world are affected by four pathogens - Batrachochytrium dendrobatidis (Bd), B. salamandrivorans (Bsal), Ranavirus and Perkinsea. A climatic context behind the dispersal of some of these diseases is hypothesized. However, the interplay between niche conservatism (NC) and climatic niche evolution (CNE), essential to understand disease evolution and dispersal, has so far received little attention. Here we show that the impacts of amphibian pathogens are intensifying as their climatic niches evolve. NC-based analyses suggest that niches of these diseases overlap, especially in Europe and East/southeast Asia (ESEA), and that all four pathogens will continue to devastate amphibians through seasonality shifts and range expansions, penetrating deeper into temperate regions and global amphibian diversity hotspots. Bd will spread over diversity-rich mountain ranges and ranaviruses will overwhelm lowlands. CNE-based analyses suggest that the earliest lineages of these diseases originated in colder regions and that some lineages subsequently evolved towards warmer climatic niches. We caution that quiescent, warm-adapted strains are likely to become widespread and novel ranaviruses adapted to local climatic conditions and new hosts are likely to emerge. These results portend the dangers of introducing pathogens into new regions given their ability to adapt to changing climate scenarios. In a climatic background conducive to most of these diseases, frequent monitoring, enhanced biosecurity measures and policy reforms are needed for disease control and mitigation.

evolutionary biology↗

bioRxiv2021

Adapting to novel environments together: evolutionary and ecological correlates of the bacterial microbiome of the worlds largest cavefish diversification

The symbiosis between a host and its microbiome is essential for host fitness, and this association is a consequence of the hosts physiology and habitat. Sinocyclocheilus, the largest cavefish diversification of the world, an emerging multi-species model system for evolutionary novelty, provides an excellent opportunity for examining correlates of host evolutionary history, habitat, and gut-microbial community diversity. From the diversification-scale patterns of habitat occupation, major phylogenetic clades (A-D), geographic distribution, and knowledge from captive-maintained Sinocyclocheilus populations, we hypothesize habitat to be the major determinant of microbiome diversity, with phylogeny playing a lesser role. For this, we subject environmental water samples and fecal samples (representative of gut-microbiome) from 24 Sinocyclocheilus species, both from the wild and after being in captivity for six months, to bacterial 16S rRNA gene profiling using Illumina sequencing. We see significant differences in the gut microbiota structure of Sinocyclocheilus, reflective of the three habitat types; gut microbiomes too, were influenced by host-related factors. There is no significant association between the gut microbiomes and host phylogeny. However, there is some microbiome related structure at clade level, with the most geographically distant clades (A and D) being the most distinct, and two geographically overlapping clades (B and C) being similar. Microbes inhabiting water were not a cause for significant differences in fish-gut microbiota, but water quality parameters was. Transferring from wild to captivity, the fish microbiomes changed significantly and became homogenized, signifying adaptability and highlighting the importance of environmental factors (habitat) in microbiome community assembly. The core microbiome of this group closely resembled that of other teleost fishes. Our results suggest that divergent selection giving rise to evolutionary novelties also includes the microbiome of these fishes, which provides a functional advantage for life in the resource-depleted cave environment. SIGNIFICANCE STATEMENTThe largest diversification of cavefishes of the world, Sinocyclocheilus, not only show that habitat, and phylogenetic clade is important in determining their gut microbiome, but also that they reach a common microbiome in captivity irrespective of their phylogenetic position, region of origin and habitat, indicating that they are adaptable in the context of microbe related changes in their environment.

microbiology↗

bioRxiv2018

Suicidal ideation and intentional self-harm in pregnancy as neglected agenda in maternal health; an experience from rural Sri Lanka

BackgroundSuicide only present the tip of the iceberg of maternal mental health issues. Only a fraction of pregnant women with suicidal ideation proceeds to intentional self-harm (ISH) and even a smaller proportion are fatal. The purpose of the present study was to determine the prevalence of depression, suicidal ideation (present and past) and history of ISH among pregnant mothers in rural Sri Lanka.\n\nMethodsWe have conducted a hospital based cross sectional study in the third largest hospital in Sri Lanka and a another tertiary care center. Pregnant women admitted to hospital at term were included as study participants. The Edinburgh Postpartum Depression Scale (EPDS), a self-administered questionnaire for demographic and clinical data and a data extraction sheet to get pregnancy related data from the pregnancy record was used.\n\nResultsThe study sample consisted of 475 pregnant women in their third trimester. For the tenth question of EPDS \"the thought of harming myself has occurred to me during last seven days\" was answered as \"yes quite a lot\" by four (0.8%), \"yes sometimes\" by eleven (2.3%) and hardly ever by 13 (2.7%). Two additional pregnant women reported that they had suicidal ideation during the early part of the current pregnancy period though they are not having it now. Four (0.8%) pregnant women reported having a history of ISH during the current pregnancy. History of ISH prior to this pregnancy was reported by eight women and five of them were reported to hospitals, while others were managed at home. Of the 475 pregnant females included in the study, 126 (26.5%) had an EPDS score more than nine, showing probable anxiety and depression. Pregnant women who had primary/post-primary or tertiary education compared to those who were in-between those two categories were at higher risk of high EPDS with a OR of 1.94 (95% CI 1.1-3.3). Reported suicidal ideation prior to pregnancy had a OR of 6.4 (95% CI 2.3-17.5).\n\nConclusionsBased on our data, we conservatively estimate around 3000 ISH annually in Sri Lanka, which should be considered as a high priority for an urgent intervention.\n\nPlain English SummaryMental disturbances are common during pregnancy. Most of the time, these are normal. However, these disturbances may become serious and lead to self-harm and suicide. In this study, we estimated the proportion of pregnant women who had depression and idea of self-harming during pregnancy.\n\nRespondents were pregnant women admitted to two large hospitals for the childbirth. They answered a list o questions about the thought of self-harm and attempts of self-harm during the present as well as past pregnancies.\n\nRespondents included 475 pregnant women. Of them, 3.1% reported that \"the thought of self-harming has occurred to them during last seven days quite a lot (0.8%) or sometimes\" (2.3%). Four (0.8%) pregnant women reported that they actually did it to some extent. Of the 475 pregnant women included in the study, 126 (26.5%) had symptoms of anxiety/depression. Level of education seemed to have an association with anxiety and depression. When women reported that they had thought of self-harm prior to pregnancy, they were about 6.4 times more likely to have depression/anxiety during the pregnancy. Adding a simple screening question (as we used in this study) during the initial pregnancy assessment to detect history of suicidal thoughts will be helpful in identification of high-risk mothers for depression and suicide.

epidemiology↗